Apparatus for continuous casting of metal strip

ABSTRACT

A twin roll continuous casting apparatus for continuously casting a metal strip through a gap of a pair of internally cooled rolls rotating in the opposite direction to each other having a pair of side dams disposed on both sides of the rolls wherein each side dam is made of an abradable refractory and forcibly fed in the casting direction, and wherein portions of the circumferential surfaces of the rolls contacting the side dams are formed into rough surfaces having an abrading ability and each of said portions having rough surfaces comprises a member removably fixed to the entity of the roll.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an improvement in a twin rollcontinuous casting apparatus for continuously casting a metal stripdirectly from a molten metal such as a molten steel.

BACKGROUND OF THE INVENTION

Well known in the art is a so-called twin roll continuous castingapparatus in which a pair of internally cooled rolls having respectivelyhorizontal axes and rotating in opposite direction to each other aredisposed parallel to each other with an appropriate gap therebetween. Apool of molten metal is formed on the circumferential surfaces (theupper halves of cylindrical surfaces in the axial directions) of therolls above the gap and the molten metal is continuously cast into ametal strip through the gap while being cooled by the circumferentialsurfaces of the rotating rolls. There has also been proposed such a twinroll continuous apparatus applied to a case of continuous casting ofsteel to produce a steel strip directly from molten steel.

When a metal strip is continuously cast through a gap between a pair ofrolls, it is necessary to form a pool of molten metal on thecircumferential surfaces of the pair of rolls above the gap therebetweenand to maintain a level of the molten metal in the pool substantiallyconstant by continuously pouring the molten metal into the pool. Inorder to form the pool of molten metal, a pair of dams are providedhaving their surfaces perpendicular to the roll axes which prevent anoverflow of molten metal along the roll axes on the circumferentialsurfaces of the rolls. These dams also serve usually to regulate thewidth of the cast strip and are referred to herein as "side dams". Inaddition to the side dams disposed at the left and right sides of therolls, a pair of front and rear gates having their surfaces along theroll axes may be erected orthogonally to the side dams on thecircumferential surfaces of the rolls so as to form a box-like pool formolten metal with the side dams and the front and rear gates. However,when the pair of rolls have sufficiently large radii respectively, thefront and rear gates along the roll axes are not always needed. In thiscase, the circumferential surfaces of the pair of rolls function as thefront and rear gates.

There are known, as the pair of side dams, movable side dams which urgea pair of endless metal belts, caterpillars and the like against bothedge surfaces of the rolls (side surfaces of the rolls perpendicular tothe roll axes) at a location of the roll gap and which move at a speedcorresponding to the casting speed. Fixed side dams are known which haveplate-like bodies of refractories fixed to left and right side surfacesof the rolls. Generally, with the latter fixed side dams, theconstitution of the apparatus is simple and the control of running isnot complicated, compared with the former movable side dams. Also knownin the art is a system of combined side dams in which fixed side damsare combined with movable dams. See JP A-62-214,835 which corresponds toU.S. Pat. No. 4,754,802.

Two systems of the fixed side dams are known. One is a system in whichthe distance between the plate-like bodies of the fixed side dams issmaller than the roll width (the length of roll from one end to theother end), and the other is a system in which the distance is the sameas the roll width. According to the former system, the pair of side damsare erected on the circumferential surfaces of the rolls such that thebottoms of the side dams slidably contact the circumferential surfacesof the rolls. According to the latter system, the side dams are fixedlyprovided so that the respective inside surfaces of the side damsslidably contact the side surfaces of the rolls, that is, the pair ofside dams sandwich the pair of rolls on the side surfaces of the rolls.

Usually, the fixed side dams are made of refractory material having agood adiabatic property. This is because the molten metal contacting theside dams has to be prevented from being solidifed on the surfaces ofthe side dams. Adiabatic refractory materials generally have inferiorwear resistance to that of solidified metal and are liable to havescratches. Thus, the fixed refractory side dams may be damaged duringthe running of the apparatus, and the increase of damages may bringabout breakout of molten metal. Further, according to the system notedabove in which the side dams are fixed so that they sandwich the rollson their side surfaces, clearances may be formed between the sidesurfaces of the rolls and the inside surfaces of the side dams slidablycontacting therewith due to pressure of the ends of the strip being castapplied at the time of passing through the roll gap. As a result, themolten meal may enter the clearances. If such troubles occur, stablecasting may no longer be continued. Accordingly, it has generally beenconsidered that refractory materials suitable for the side dams shouldhave a good wear resistance and the highest possible strength.

During the continuous casting, a portion of molten metal in the poorforms thin solidified shells respectively on the surfaces of therotating rolls, and then these shells pass through the gap between thetwin rolls while growing along with rotation of the rolls. At this time,the solidified shells are depressed (rolled) at a portion in theneighborhood of the smallest gap between the rolls to form into a metalstrip of a predetermined thickness. Thus, owing to this depression(rolling), the solidified shells tend to expand widthwise near the rollgap. As a result, the ends of the cast strip apply large pressure to theside dams. In the case or the movable side dams wherein the side damsare moved at a speed corresponding to the casting speed, a problem offriction between the side dams and the ends of of the cast strip is notsubstantially posed. In the case of the fixed side dams, however, largefriction is inevitably generated between between the ends of the movingcast strip and the fixed side dams. The large friction can cause damageto the refractory side dams, occurrence of cracking and undesirablydeformation of the ends of the cast strip, formation of clearancesbetween the side surfaces of the rolls and the inside surfaces of theside dams slidably contacting therewith, and entrance of molten metalinto the clearances so formed, all of which hinder stable continuouscasting. These problems are especially serious in the case of continuouscasting of steel wherein the material involved is higher melting and hashigher strength, when compared with cases wherein lower melting and mildnon-ferrous metals are concerned.

In Japanese Patent Application No. 62-84,555 (published s JPA-63-252,646 on Oct. 19, 1988, after the priority date of the presentinternational application, that is, Jul. 22, 1988; the correspondingU.S. patent application was issued as U.S. Pat. No. 4,811,780 on Mar.14, 1989.), we have proposed as a solution to the above-discussedproblems a continuous casting apparatus for metal strip which may besaid "abradable dam system" or "semi-movable dam system" intermediatebetween "movable" and "fixed" dam systems. According to our priorproposal. a refractory material capable of being well abraded is used asthe material for the side dams, contrary to the prior art concept thatrefractory materials suitable for the side dams should have a good wearresistance and the highest possible strength. The abradable side damsare forcibly fed or moved in the casting direction during the castingwhile being frictionally abraded by slidably contacting surfaces of therotating rolls and ends of the strip being cast. Repeated runs ofcontinuous casting by the abradable dam system have indicated thatfurther improvements are desired for a further stable running ofcontinuous casting.

OBJECT OF THE INVENTION

The invention intends to improve the continuous casting apparatus of anabradable dam system which we have previously proposed in JapanesePatent Application No. 62-84,555 for the purpose of solving the problemsdiscussed above.

DISCLOSURE OF THE INVENTION

An apparatus for continuously casting a metal strip according to theinvention comprises a pair of internally cooled rolls rotating in theopposite direction to each other and disposed parallel to each otherwith their axes held horizontally. A pair of side dams for forming apool of molten metal on the circumferential surfaces of the pair ofrolls are provided, said side dams bring disposed with a spaceapproximately corresponding to the width of a metal strip to be cast andso that at least a portion of the bottom of each dam may contact thecircumferential surfaces of the rolls so as to allow at least a portionof the thickness of each side dam to be located on the circumferentialsurfaces of the rolls. A least those portions of said side dams whichcome in contact with the circumferential surfaces of the rolls arecomposed of a refractory material capable of being well abraded.mechanisms for forcibly feeding said side dams in the casting directionat a predetermined speed are provided, thereby continuously casting themolten metal in the pool into a metal strip through a gap between thepair of rolls while abrasively wearing said side dams at said portionscontacting the circumferential surfaces of the rolls, characterized inthat portions of the circumferential surfaces of the rolls contactingthe side dams are formed into rough surfaces having an abrading ability.Each of said portions having rough surfaces comprises a member removablyfixed to the entity of the roll. In preferred embodiments according tothe invention, the member removably fixed to an entity of the roll is adisc having a roughened circumferential surface or a ring belt having aroughened outside surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing principal portions of an embodimentof the apparatus according to the invention;

FIG. 2 is a perspective view showing an example of a shape of therefractory side dam in the apparatus of FIG. 1;

FIG. 3 is a fragmentary perspective view of a disc having a roughenedcircumferential surface which is removably fixed to the entity of theroll,

FIG. 4 is a fragmentary perspective view of a ring belt having aroughened outside surface which is removably fixed to the entity of theroll,

FIG. 5 is a perspective view of the side dam in the apparatus of FIG. 1under the condition where the degree of abrasion of the dam is small atan early stage of the casting process;

FIG. 6 is a perspective view of the side dam in the apparatus of FIG. 1under the condition where the degree of abrasion of the dam is proceededin the casting process;

FIG. 7 is a schematic cross-sectional partial view of the apparatus ofFIG. 1, showing a state of casting, as viewed in a plane parallel to theplane of the cast strip; and

FIG. 8 is a schematic cross-sectional partial view of another embodimentof the apparatus according to the invention, as viewed in a planeparallel to the plane of the cast strip.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described in detail with reference to thedrawings.

Referring to FIG. 1, reference numerals 1a, 1b designate a pair ofinternally cooled rolls rotating in the opposite direction to each other(the rotational directions of both rolls are shown by arrows) andopposed parallel to each other with their roll axes held horizontally.Reference numeral 2 designates a molten metal in a pool formed on thecircumferential surfaces R of the pair of rolls 1a, 1b. Referencenumerals 3a, 3b designate side dams and 4 a cast strip, respectively.

In either of the illustrated embodiments the rolls 1a, 1b are internallycooled with water. More specifically, the rolls 1a, 1b are formed on theinside of drums constituting the circumferential surfaces R with coolingwater paths (not shown). The circumferential surfaces R are adapted tobe cooled to a predetermined temperature by water passing through thecooling water paths. Cooling water is supplied to and drained from thecooling water path on the inside of the circumferential surface Rthrough a shaft of each roll. Thus, the roll shaft is of a double pipestructure with an inner pipe serving as a supply pipe and an annularpipe path formed between outer and inner pipes serving as a drain pipe.In the interior of the roll, the cooling water supply pipe which is theinner pipe is connected to an inlet of the cooling water path providedinside the circumferential surface R, while the annular pipe path isconnected to a cooling water outlet. When cooling water is continuouslysupplied from a pump P into the inner pipe as shown in FIG. 1, thesupplied cooling water is circulated through the cooling water pathlocated inside the circumferential surface R and then drained throughthe annular pipe path. The illustrated apparatus is constructed so thatthe operation of passing cooling water may be carried out even in therunning of the apparatus.

The side dams 3a, 3b are grasped by metal side dam cases 5a, 5b mountedon the outside surfaces of the side dams and moved in the castingdirection. The side dams 3a, 3b themselves are made of a refractorymaterial having a good abradability. The shape of each side dam is asshown in FIG. 2. One inner portion W₁ of the whole thickness Wcorresponds to a thickness of a portion installed on the circumferentialsurfaces R of the rolls and the other outer thickness W₂ corresponds tothe thickness of a portion installed out of the the circumferentialsurfaces of the rolls, as shown in FIG. 2. Namely, the inner thicknessportion W₁ has bottom surfaces 6, 6' worked to have curved surfacescorresponding to the circumferential shapes of the rolls 1a, 1b and theouter thickness portion W₂ is shaped to form portions 7, 7' slidablycontacting side surfaces of the rolls 1a, 1b and extending to portionslower than the bottom surfaces 6, 6' . Materials constituting the sidedams 3a, 3b should be not only adiabatic enough to prevent the moltenmetal from being solidified on inside surfaces of the side dams 3a, 3b,but also capable of being abraded by rough surfaces 10 of thecircumferential surfaces of the rolls 1a, 1b. Further, they arepreferably properly abraded by ends of the strip being cast. Examples ofsuch suitable materials include, for example, adiabatic bricks, ceramicfiber boards and boron nitride (BN) which have goo abradability, thatis, a capability of being well abraded.

As shown in FIG. 1, on the outer surfaces of the refractory side dams3a, 3b which are shaped as shown in FIG. 2 are mounted the metal sidedam cases 5a, 5b to cover wholly the outer surfaces for grasping theside dams 3a, 3b. In this case, the curvedly worked bottom surfaces 6,6' of the thickness portion W₁ contact the circumferential surfaces R ofthe rolls 1a, 1b, and the inner surfaces 7, 7' of the thickness portionW₂ slidably contact the side surfaces of the rolls 1a, 1b. The side damcases 5a, 5b are supported by a plurality of struts 8 with screwsthrough nuts 9 fixed to the case side. Each strut 8 is rotated about itsown axis to move the side dam cases 5a, 5b in the casting direction.Thus. the side dams 3a, 3b during the running of the apparatus arelowered together with bottom surfaces 6, 6' being abraded by thecircumferential surfaces of the rotating rolls. In addition to themechanical engagement of the side dam cases 5a, 5b with the side dams3a, 3b, they are preferably adhesively bonded together at the interfacesbetween them. Thus, the abradable side dam refractories with generallylow tensile strength are reinforced. A system of continuously loweringthe side dams is preferably used in a mechanism for moving the side damsdownward. However, an intermittent moving system for repeatedly loweringand stopping the side dams, or a system for lowering with slightoscillation may also be used, depending on particular cases. In anycase, the lowering speed of the side dam is preferably controlled inaccordance with a detected signal on a lowering amount of the side damor a width of the strip being cast.

Portions of the circumferential surfaces of the rolls slidablycontacting the bottom surfaces 6, 6' of the side dams 3a, 3b are formedinto rough surfaces having an abrading ability. The rough surfaceportions (4 portions) are designated by reference numeral 10 in FIG. 1.If the roughness and hardness of the portions 10 are properly selectedaccording to the material of the side dams 3a, 3b and castingconditions, abrasion of the bottom surfaces 6, 6' of the side dams 3a,3b adequately proceeds during casting. It is desirable that the adequateabrasion conditions are stationary and do not change with time.

For this purpose, in the apparatus according to the invention, each ofthe roughened surface portion 10 having an abrading ability is made intoa member which can be removably fixed to an entity of the roll. By doingso, it is possible to provide a roughened surface having a desiredabrading ability, irrespective of the material of the circumferentialsurface of the roll proper, and repair and exchange of the roughenedsurface can be carried out at will.

FIG. 3 shows a disc 11 which is removably fixed to the entity of theroll 1. The disc 11 has a diameter substantially the same as that of theentity of the roll 1, a thickness substantially the same as a slidablycontacting width of the bottom surfaces 6, 6' of the side dam, and aroughened circumferential surface 10. Thus, by mounting the disc 11having the roughened circumferential surface 10 on the side surface ofthe roll coaxially with the roll, there may be provided a surface forabrading the bottom surfaces 6, 6' of the side dams. The disc 11 may beconveniently fixed to the entity of the roll 1 by screwing bolts 14(FIG. 1) through holes 13 provided in the disc 11 into threaded femaleholes formed in the side surface of the roll entity 1. If desired, thedisc 11 may be divided into several segments. Namely, it may be radiallydivided into fan-shaped segments, which are to be individually fixed tothe entity of the roll to form a disc shape as a whole. In the conditionthat the disc 11 is fixed to the roll entity 1 in position, the insidesurfaces 7, 7' of the W₂ portion of the side dam shown in FIG. 2 are tocome in slidable contact with an outer disc surface of the disc 11 (sidesurface of the roll) during the running of the apparatus. Thus, in somecases the outer disc surface of the disc 11 may also be made roughenedso that it may appropriately abrade the inside surfaces 7, 7' of theside dam.

FIG. 4 shows a ring belt 16 which is removably fixed to the rollentity 1. The ring belt 16 has a roughened outside surface 10. On thateach edge portion of the circumferential surface of the roll entity 1,which comes in slidable contact with the bottom surface 6, 6' of theside dam, there is formed a shallow groove 17 having a widthcorresponding to the width of slidable contact and a depth correspondingto the thickness of the belt 16, in which groove 17 the ring belt 16 ismounted. The ring belt 16 may be fixed to the roll entity 1 by threadedcoupling engagement of bolts through small holes in the belt ring withsmall threaded female holes 18 formed on the roll entity side. Ifdesired the ring belt may be circumferential divided into 2, 3 or 4segments, which form a ring shape as a whole, when individually mountedon the roll entity in position.

Materials different from that constituting the circumferential surface Rof the roll entity can be used for constituting the circumferentialsurface of either disc 11 or ring belt 16. The material of thecircumferential surface R of the roll is inherently selected inconsideration of required heat conductivity and formation of soundsolidified shells. Accordingly, from the view point of sufficientabrading function it is often advantageous to form the abrading roughsurface of a material other than that of the circumferential surface Rof the roll entity instead of roughening the circumferential surface Rof the roll. By doing so, the rough surface can be prepared separatelyfrom the preparation of the rolls, and can be exchanged for repair orrenewal. An abrading rough surface may be formed on the circumferentialsurface of the disc 11 or ring belt 16 preferably by providing a layerof a hard material followed by roughening the so provided hard layer.The layer of a hard material may be formed advantageously by flamespraying of a hard metal such as Ni-Cr alloys, carbon steels andstainless steels, a ceramic such as Cr₂ O₃, TiO₂, Al₂ O₃ and ZrO₂, or acermet such as ZrO₂ -NiCr, Cr₃ C₂ -NiCr and WC-Co. If a flame spraycoating is built under such conditions that surface depressions andextrusions may be naturally formed by deposition of flame sprayedparticles, the resulting flame spray coating as such has a roughenedsurface which can perform the abrasive wear of the abradable side dam.To improve the adhesion of the flame spray coating to the substrate(surface to be flame sprayed), some kinds of substrate may be preferablysubjected to pretreatment prior to flame spraying. For example, thesubstrate may be plated with metal prior to flame spraying. Furthermore,the substrate may be roughened by sand blasting, and then flame sprayed.In place of forming a rough surface by flame spraying, a rough surfacemay be formed by forming a layer of a hard metal by plating androughening the so formed hard layer. Examples of suitable hard metalinclude Ni and Ni-base alloys, Ni-Fe alloys. Cr and Cr-base alloys andFe alloys. If the surface of the plated metal is smooth, it should beroughened, for example by emery polish or sand blasting.

In the apparatus according to the invention, those portions of thecircumferential surfaces of the rolls which come in slidable contactwith the bottom portions 6, 6' of the side dams are constructed of theremovable members 11, 16 which have a roughened surface 10 of a hardmaterial and are removably fixed to the roll entity 1. The material ofthe roughened surface 10 can suitably selected so that the roughenedsurface may not be deteriorate and may maintain a good abrading abilityfor a prolonged period of time. Furthermore, the members 11, 16 areexchangable. By the way, a reference numeral 18 designates a brush forcleaning the rough portions 10. The brush 18 disposed in abuttingengagement with the rough portions 10 acts to remove abraded powdergenerated by rotation of the rolls and attached to the rough surface ofthe portion 10, thereby preventing the rough surface from choking upwith the abraded powder.

FIG. 5 shows the internal surface condition of the side dam according tothe invention at an early stage of the casting process. Side ends ofsolidified shells formed on the respective surfaces of the internallycooled rolls contact the internal surface of the side dam on the levelsshown by reference symbols a, 1' in FIG. 5, and are combined together atpoint A. That is, a portion of molten metal in the pool is cooled on thesurface of each roll and then solidified to thin shells. The solidifiedshells so formed on the surfaces of the respective rolls grow andcombine together along with the rotation of the rolls, and the combinedshells are rolled through the gap between the rolls to a predeterminedthickness. During the course of this, ends of the solidified shells comein contact with the internal surface of each side dam on the level shownby a, a'. The initial configuration of the side dam (before it isabraded by running of the apparatus) is preferably determined such thatthe confluence A of the solidified shells (the position where thesolidification of the shells is completed) will be located below thelower edge 20 of the side dam. However, during the casting process, theconfluence A may be moved to a position A' above the position of thelower edge 20 due to variations in casting conditions. In this case, thewidthwise expansion of the strip (the solidified metal strip which haspassed the confluence) will abrade the corresponding (lower edge)portions of refractories. Unless the side dams are lowered under suchconditions, the strip width is gradually increased. If the strip widthexceeds the roll width, the strip formed may have a dog bone likecross-section with ends coming from the exceeding portions swollen, andin the further proceeding of casting, the side dams will be damaged,resulting in breakout of molten metal. Such situations can be avoidedwith the apparatus according to the invention, in which the dams of anabradable refractory material are lowered at a predetermined speed, andthus, new surfaces of the side dams are successively lowered even if theedge portions of the dams are abraded off by the ends of the strip beingcast, and, in consequence stable casting of a metal strip with apredetermined width can be realized with the apparatus according to theinvention.

FIG. 6 shows the internal surface of the side dam when it has beenconsiderably lowered in the proceeding of casting. While the bottomsurfaces 6, 6' and lower edge 20 of the side dams have been abraded bythe rough surfaces 10 of the rolls and the side ends of the cast strip,respectively, and their positions have moved upward relative to theinitial positions shown in FIG. 5, the lower edge 20 has been abraded bythe strip ends into a somewhat slant condition. Below the lower edge 20,there is exposed an inside surface 21 of that portion of the side damwhich extends beyond the width of the roll. This surface 21 mayadditionally serve to prevent leakage of molten metal. Incidentally,under the condition shown in FIG. 6 again, side ends of solidifiedshells formed on the respective surfaces of the rolls contact theinternal surface of the slide dam on the levels a, a' and are combinedtogether at the confluence A, as is the case under the condition shownin FIG. 5.

FIG. 7 shows schematically the process of casting corresponding to thatin FIG. 6 As shown in FIG. 7, the lower edges 20 of the side dams may bemaintained in the positions above the narrowest gap (at the center levelof roll shaft 22) between the twin rolls by moving (lowering) forciblydownward the side dams, while the lower edges 20 are ground into slopedshapes. Thereby, the widthwise expansion of the strip which has passedthe confluence A of the solidified shell is restrained. If the side damsare set to certain fixed positions without lowering them, it will beunderstood that the internal surfaces of the side dams will besuccessively ground by the shells and strip ends 23 which are expandedwidthwise at the narrowest gap and eventually the molten metal will leakfrom the side dam portions which are ground when the strip width exceedsthe roll width. This occurs not only in the case of refractories withsatisfactory abradability, but also in the case of general refractories.When refractories having antiwear property are used, cracks take place,resulting in more dangerous conditions. Contrary to the prior conceptionof using refractories with antiwear property, the invention uses theside dams made of refractories which are liable to be ground. Then, theside dams forcibly lowers to positively grind refractories. As a result,a stable casting may be carried out without presenting the abovementioned problems. By employing such lowering speed, the bottomsurfaces 6, 6' of the side dams contacting the circumferential surfacesof the rolls and the internal surfaces (substantially near the loweredges 20) of the side dams contacting the shells and cast strip ends areground while maintaining the shapes of these bottom and internalsurfaces of the side dams substantially similar. More particularly, suchlowering speed is employed such that the grinding speed of the shellsand strip ends near the lower edges 20 does not exceed the grindingspeed of the bottom surfaces 6, 6' of the side dams, i.e. the side damsare allowed to lower such that the latter speed becomes higher than theformer speed. In addition, the abrading tough surface 10 according tothe invention is prepared from a material different from that of theroll entity 1 and removably is fixed to the roll entity 1, whereby apower of abrading the side dams may be enhanced, maintenance of theapparatus my become easy, and optimum abrading conditions may bestationarily maintained, thereby ensuring a still stable continuouscasting.

Further, while heretofore has been described an example of the side damshaving one portion of thickness within the roll width and the otherportion of thickness outside the roll width, the invention may also beapplied to a system in which the whole thickness of the side dam comeswithin the roll width. FIG. 8 shows this example. As shown by thearrows, in this case again, the side dams 3a, 3b are moved downward andthe side dams 3a, 3b themselves are of course made of refractories withsatisfactory abradability.

We claim:
 1. An apparatus for continuously casting a metal stripcomprising a pair of internally cooled rolls rotating in the oppositedirection to each other and disposed parallel to each other with theiraxes held horizontal, a pair of side dams for forming a pool of moltenmetal on the circumferential surfaces of the pair of rolls, said sidedams being disposed with a space approximately corresponding to thewidth of a metal strip to be cast and so that at least a portion of thebottom of each dam may contact the circumferential surfaces of the rollsso as to allow at least a portion of the thickness of each side dam tobe located on the circumferential surfaces of the rolls, at least thoseportions of said side dams which come in contact with thecircumferential surfaces of the rolls being composed of a refractorymaterial capable of being well abraded, and mechanisms for forciblyfeeding said side dams in the casting direction at a predeterminedspeed, thereby continuously casting the molten metal in the pool into ametal strip through a gap between the pair of rolls while abrasivelywearing said side dams at said portions contacting the circumferentialsurfaces of the rolls, characterized in that portions of thecircumferential surfaces of the rolls contacting the side dams areformed into rough surfaces having an abrading ability; and each of saidportions having rough surfaces comprises a member removably fixed to theentity of the roll.
 2. The apparatus for continuously casting a metalstrip according to claim 1 wherein said member removably fixed to theentity of the roll comprises a disc having a roughened circumferentialsurface.
 3. The apparatus for continuously casting a metal stripaccording to claim 1 wherein said member removably fixed to the entityof the roll comprises a ring belt having a roughened outside surface.